One of the most difficult problems in simulating natural history in the laboratory is deciding what to simulate. It would be useless to import the habitat intact because the advantages of the labo­ ratory-reduction in detail, precision of observa­ tion, and control of variables-would be lost. To decide what to import, one must have a model of behavior. The veridicality of the simulation depends upon the perspicacity of this model. In our work, we have taken as fundamental the assumption that behavioral decisions depend upon an analysis of costs and benefits, and we have combined this concept with a 24-hr, closedeconomy, operant procedure in what will be called a “foraging paradigm.” In this essay we will contrast traditional laboratory paradigms with our foraging paradigm and we will contrast the depletion/repletion models of feeding and drinking, which focus on homeostatic mecha­ nisms, with our longer-term perspective, which focuses on function. First we will discuss how our paradigm differs from others, and then we will review the laws that we have discovered.